The present invention relates to a silver iodide fine grain emulsion and a lightsensitive silver halide emulsion containing lightsensitive silver halide grains produced through a step in which silver halide grains are grown by adding the above silver iodide fine grain emulsion.
Generally, silver halide grains are produced by reacting an aqueous solution of a silver salt with an aqueous solution of a halide in a colloidal aqueous solution in a reaction vessel. Single jet method and double jet method are known. In the former method, a protective colloid dispersion medium such as gelatin and an aqueous solution of a halide are placed in a reaction vessel, and, while agitating these, an aqueous solution of a silver salt is added thereto for a given period of time. In the latter method, an aqueous solution of gelatin is placed in a reaction vessel, and an aqueous solution of a halide and an aqueous solution of a silver salt are added thereto for a given period of time. When a comparison is made, it is found that the double jet method is superior to the single jet method in that silver halide grains with narrow grain size distribution can be obtained and that the halogen composition thereof can freely be changed in accordance with the growth of the grains.
It is known that the nucleation and growth of silver halide grains are extensively varied depending on the concentration of silver ions (halide ions) or concentration of silver halide solvent in a reaction solution, the degree of supersaturation, the temperature, etc. Any nonuniformity in the concentration of silver ions or halide ions produced by the silver salt aqueous solution or halide aqueous solution placed in the reaction vessel leads to the occurrence of supersaturation and solubility distributions in the reaction vessel, depending on individual concentrations. Therefore, nonuniformity occurs in the nucleation and growth of silver halide grains.
In particular, it is known that the above nonuniformity is conspicuous in the formation of silver halide grains containing silver iodide. In the emulsion comprising silver halide grains containing silver iodide, it is known that intergrain differences of halogen composition are large due to the variation of silver iodide content among individual silver halide grains and that, even within the same grain, the silver iodide distribution has a bias depending on portions of the grain. Y. T. Tan and R. C. Baetzold presented before the 41st annual meeting of SPSE such a prospect that the iodine within silver iodobromide crystal grains tends to form a cluster on the basis of calculated energy states of silver halide grains. It is presumable that this property of iodine causes the above nonuniformity.
The above nonuniformity is considered to be a factor determining the performance of a silver halide emulsion containing silver iodide. In the art to which the invention pertains, various studies have been made with a view toward resolving the nonuniformity.
The method in which an aqueous solution of a silver salt and an aqueous solution of a halide are rapidly and homogeneously mixed together for resolving the above nonuniformity of silver ion or halide ion concentration is disclosed in, for example, U.S. Pat. No. 3,415,650, GB 1,323,464, U.S. Pat. No. 3,692,283, Jpn. Pat. Appln. KOKOKU Publication No. (hereinafter referred to as JP-B-) 55-10545 and Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-) 57-92523. However, the intragrain or intergrain nonuniformity of silver iodide content among silver halide grains, which nonuniformity occurs during the step of forming silver halide grains containing silver iodide, has not been resolved.
On the other hand, JP-A-1-183644 discloses the technique in which silver iodide which contributes to grain formation is fed in the form of a fine grain emulsion in order to resolve the intragrain or intergrain nonuniformity of silver iodide content among silver halide grains containing silver iodide. In the specification of this literature, it is recited that a lightsensitive silver halide emulsion with high sensitivity can be obtained by resolving the intragrain and intergrain nonuniformity of silver iodide content.
Further, JP-A-3-213845 and JP-A-8-29904 disclose the technique in which silver iodide which must be fed for introducing dislocation lines in tabular silver iodobromide grains is fed in the form of a fine grain emulsion. In these patent publications, the reason for using a fine grain emulsion in grain formation would be that it is intended to attain a performance enhancement by minimizing the intergrain nonuniformity.
When the feeding of silver iodide which contributes to formation of grains of the desired silver halide emulsion is conducted in the form of a fine grain emulsion, the silver halide concentration of the fine grain emulsion is a principal factor which influences the productivity of the desired silver halide emulsion. The higher the silver halide concentration of the fine grain emulsion, the greater the amount of silver halide charged in a reaction vessel with limited volume to thereby enable a productivity increase. Moreover, with respect to the handling such as storage, conveyance or weighing of the fine grain emulsion which is needed during a period from after preparation of the fine grain emulsion to production of the desired silver halide emulsion, the higher the silver halide concentration of the fine grain emulsion, fundamentally the greater the attained advantage. That is, when the silver halide concentration is high, the volume/weight of the emulsion becomes small, so that not only can the scale of facilities required for storage, conveyance, weighing, etc. be compacted but also labor workload can be reduced.
However, the heightening of silver halide concentration of the fine grain emulsion has not been sufficiently studied, and the current situation is such that information about the same is poor on the published patents, literature, etc. In particular, information about the increased silver iodide concentration of a silver iodide fine grain emulsion is poor. As a result of the inventors' studies, it has been found that, when the silver iodide concentration of the silver iodide fine grain emulsion is increased, there is such a problem that the storage thereof in a dissolved state or in a refrigerated and set state is accompanied by the occurrence of emulsion grain aggregation with the passage of time. One method of enabling avoiding this problem is provided by the technique disclosed in JP-A-2-172816. This technique comprises preparing a fine grain emulsion in a mixing vessel disposed outside a reaction vessel, immediately thereafter concentrating the fine grain emulsion by passing it through a concentrator in which an ultrafiltration membrane or a semipermeable membrane is used and immediately thereafter placing the concentrate into the reaction vessel. However, this method necessitates a mixer for preparing the fine grain emulsion per reaction vessel and also a concentration unit for concentrating the fine grain emulsion, which includes an ultrafiltration membrane or a semipermeable membrane, a pressure control valve, a pressure sensor, etc. Thus, the problem is encountered such that the emulsion producing apparatus is extremely complicated and, accordingly, the load relating to maintenance of the emulsion producing apparatus is increased.
Therefore, there is a demand for the preparation of a silver iodide fine grain emulsion in which the concentration of silver iodide is high, which is excellent in the stability during the storage in a dissolved state or in a refrigerated and set state and whose aggregation behavior with the passage of time is slight.